The following information is an extract from PEW recommendations on Arctic Oil Spill Prevention, Response, and Safety in the U.S. Arctic Ocean published during September 2013. The design of the drilling rig, the blowout preventer, or BOP, and cementing practices are all essential to safe drilling operations and accident prevention. Drilling rigs must be designed and operated to meet the Arctic conditions they will encounter. Due to the remote nature of Arctic drilling operations, rigs must be self-sufficient and carry a minimum level of well control materials such as drilling mud, cement, and extra fuel.
Nearshore areas of the Chukchi and Beaufort seas have landfast ice. By the end of winter, landfast ice is typically 5 to 7 feet thick, extending seaward to a depth of about 60 feet.34 In the nearshore shallow waters of the Beaufort Sea, there are two potential exploration drilling seasons. The first is during open water in summer. The second is during landfast ice conditions in winter. Historically, ice-resistant, bottom-founded (fixed to the seafloor) drilling systems have been used in nearshore areas during the summer, or ice- or gravel-reinforced islands were constructed with drilling units on top of them for winter drilling.
In the deeper waters of the Beaufort and Chukchi seas, exploration drilling occurs during open water in summer, using floating drilling rigs. Here, the ice is moving throughout most of the year and the amount of thick multiyear ice increases with increasing distance from shore. Therefore, drilling rigs must be equipped to encounter thick multiyear ice floes, even during summer drilling seasons.
Performance standards for Arctic OCS drilling rigs
Drilling rig selection is a critical step for Arctic oil and gas exploration and for delineation well drilling—drilling wells to define the size of the oil reservoir. Operators must select a drilling rig that is suitable to operate in the conditions the rig may encounter while drilling the planned well and be able to provide relief well drilling assistance to other rigs working in the Arctic to control a well blowout.
The biggest concern is a late-season well blowout that requires drilling to continue into late fall-early winter ice, which would require a Polar Class rig. Constantly moving a rig off the drilling site to avoid ice will not be an option when a blowout occurs, and a relief well drilling rig must remain in position to drill a relief well in the weather and ice conditions that may be present during the late fall and early winter. These kinds of drilling operations would require a Polar Class rig. (see table below, source: International Association of Classification Societies)
Mobile Offshore Drilling Units, or MODUs, are floating rigs or “drillships” used for Arctic exploration drilling. MODUs are given a Polar Class rating based on hull strength and ability to operate in ice. MODUs working in Arctic waters, even in summer, require icebreaker support for ice management and must be capable of transiting thick first-year Arctic ice, with the potential to encounter thicker and harder multiyear ice. Arctic drillship design must include a hull shape that:
- Minimizes ice loads, or the weight and stress of ice against a vessel.
- Prevents ice accumulation in the “moon pool” area (where drilling equipment passes through, typically located in the center of the MODU).
- Prevents ice damage to propulsion systems.
- Safely transits ice-infested waters.
The International Association of Classification Societies classifies equipment using the term Polar Class to describe the type of ships constructed of steel, intended for navigation in ice-infested waters, and with respect to operational capability and strength.
The International Maritime Organization (IMO) “Guidelines for Ships Operating in Polar Waters” also uses the term Polar Class vessels to address the additional risk imposed on vessels by the harsh environmental and climatic conditions in polar waters. The IMO 2010 Guidelines states that “only ships with a Polar Class designation or comparable alternative standard of ice-strengthening appropriate to the anticipated ice conditions should operate in polar ice-covered waters.”
Polar Class designations range from Polar Class 1, the strongest vessel that is capable of year-round operation in all polar waters in thick ice, to Polar Class 7, the lowest-strength vessel capable of operating in summer and autumn’s new, thinner ice. These ratings are applied to all types of vessels operating in polar waters, not just MODUs.
As shown in the table above, MODUs operating in summer and autumn with first-year ice should meet at least a Polar Class 7 standard. MODUs operating later in the year must meet a higher Polar Class standard. Once exploration and any further drilling required to delineate the hydrocarbon formation is complete, a yearround OCS production facility may be installed. A development drilling rig would likely be installed on top of the year-round OCS production facility to drill the remaining production wells. The development drilling rig would need to be capable of withstanding the Arctic weather conditions in which it plans to operate, meaning that like the production facility, it must be enclosed and winterized to withstand year-round weather.
PEW’s recommendations
- Arctic Outer Continental Shelf (OCS) oil and gas operators should be required to use purpose-built Polar Class drilling rigs.
- The rig should hold a valid certification from a recognized classification society throughout the operation that verifies the drilling rig is appropriate for the site, intended use, and season of operation.
- An independent third-party expert should be required to inspect the rig and certify that it meets the qualifications for the Arctic conditions it may encounter.
Arctic OCS BOP standards
The offshore well blowouts in the East Timor Sea off Australia in 2009 and in the Gulf of Mexico in 2010 are reminders of the critical importance of high-quality, properly operating blowout preventer, or BOP, systems and the need for redundant backup systems. Blowout preventers are critical well control devices, which means their age and condition are key factors in performance and reliability. There is no age limit on BOP systems in US Interior Department regulations, meaning these systems operating in the Arctic could be several decades old.
PEW’s recommendations
- Arctic BOP systems should be inspected and verified by an independent third-party expert prior to initial use and after major repairs, and be re-certified at least every five years.
- Redundant BOP systems should be installed to ensure the BOP functions in an emergency. This includes backup BOP systems on-site; double-blind shear rams in each BOP to close in the well; multiple access points to control the BOP in case one access point is blocked or does not function; and a means to remotely operate the BOP if a well control incident impedes direct access to the BOP.
Arctic well cementing practices
Cement is a critical structural component of a well. Cement secures the drill pipe and provides a barrier for hydrocarbons to prevent a blowout. Oil and gas leaks can occur due to poor cementing practices, such as installing poor-quality cement, contaminating the cement with drilling mud, installing cement incorrectly, or damaging the cement while working on the well. Several of these cement integrity deficiencies contributed to the Deepwater Horizon blowout.
In the Arctic, cold soil compromises cement strength, which means specialty cements are required to ensure a strong, durable barrier. Conventional cements used in temperate locations are not satisfactory in Arctic wells because they freeze before they can set up sufficient compressive strength. Thawing of frozen soils must also be prevented. Thawing can increase the volume of cement needed, cause the well to subside, and create stress on the well piping.
Methane gas hydrates are commonly encountered when drilling Arctic wells. Methane gas hydrates are essentially crystals of methane gas trapped in ice and typically found relatively shallow, hundreds of feet deep. Methane gas hydrates become unstable, changing from a solid to liquid and gas as temperature and pressure changes occur during the cementing process. The intrusion of methane gas hydrates into cement can weaken the cement, creating spaces that allow hydrocarbons to pass through the cement, potentially resulting in well control incidents if not considered in the well design.
Electronic tools can be lowered into the wellbore to examine the cement quality. The Interior Department does not currently require these cement evaluation tools to be run on each Arctic well.
Photo above: A blowout preventer, or BOP, system—shown here—is designed to seal off a runaway well. A well-designed, properly operating BOP is essential to safe drilling operations and accident prevention. Photo credits: Jose Mandojana.
PEW’s recommendations
- Arctic-specific cementing standards should account for permafrost and methane gas hydrates.
- A cement evaluation tool, cement bond log, or equivalent logging tool should be used to verify successful cement placement in all Arctic OCS wells.
Source: PEW
Officer of the Watch 
Leave a Comment